I am the minivan owner... I find that my WPM did not move significantly. In fact, I would argue that for the most part my typing speed is the same. Now, when it gets to coding, or {}, [], things slow down just a tiny bit, but with todays editors, this can be minimized.
I will admit, I have been in IT for many years. I feel like unless you are an accountant, or someone that has to hit {} [] constantly and can not deal with macros, that the 60%, 40% keyboards help a lot. Most CS/sysadmin/engineer type people are good with layering anyway.
I will say this, on a normal keyboard, you have to hit shift to do a few odds and ends. On a 40%, you would be amazed at the speed that you pikcup "oh, hey, {} and [] are over here, just I have to hold down this one key, just like shifting on an normal keyboard... ok, I get it" and then by week two you no longer think about it. Just my $0.02. I did, however, test my typing speed on one of those online things. I really did not change much after about a month from my previous keyboard to the minivan.
